1. Field of the Invention
The present invention relates to a hybrid-type stepping motor, and more specifically, to new improvements in the hybrid-type stepping motor in which the winding and placement of coils are facilitated by employing a solenoid-on-bobbin winding method and the density of coils is increased to provide a high efficiency and low cost design.
2. Description of the Related Art
In the hybrid-type stepping motor conventionally used, as shown in FIG. 1, a rotor yoke 9 as an outer rotor is rotatably supported by a stator yoke 6, and a coil is wound around each tooth 7 of the stator yoke.
FIG. 2 shows the structure, disclosed by Nikkei Mechanical published Aug. 13, 1984, in which a rotor yoke 9 is rotatably supported between an inner stator yoke 6A and an outer stator 6B and an unshown coil is directly wound around each of the teeth 7 of the stator 6A, 6B. As shown in FIG. 3, a rotary shaft 1 is rotatably supported at a pair of bearings 2, 3 secured on both ends of a casing 4. A generally ring-shaped stator yoke 6 having a stator coil 5 is mounted on the inner surface 4a of the stator casing 4. A plurality of stator teeth 7 are spaced regular intervals apart circumferentially around the inner circumference of the stator yoke 6. Disposed between the bearings 2, 3 are ring-shaped first and second rotor yokes 9, 10 which are arranged in a unitary body on the rotary shaft with a magnet 8 therebetween, and the rotor yokes 9, 10 have on their circumferences, a plurality of rotor teeth 9a, 10a, and the rotor yokes 9, 10 alternate with each other in polarity. By supplying a driving pulse from an unshown driving circuit to the stator coil 5, the rotor yokes 9, 10 rotate stepwise.
The prior art hybrid-type stepping motor thus constructed has the following problems.
In the hybrid-type stepping motor having the rotor yokes having each magnet interposed therebetween as shown in FIG. 3, the stator coil wound around each tooth of the stator yoke is positioned inside the casing, and thus coil winding to each tooth is difficult and increasing the density of coil is difficult, too. In the structures shown in FIG. 1 and FIG. 2, the coil should be directly wound around each tooth, and thus the same above problems arise.